There are many instances where the flow of a liquid medium through relatively small diameter pliable plastic tubing systems is regulated by the incorporation in the tubing system of a flow control device of comparatively small size and light in weight so that the device is capable of being supported or suspended in place solely by the tubing itself. In the medical field, for example, such type flow control devices are commonly employed to regulate the flow of medical fluids through intravascular catheter systems which customarily employ elastically deformable or compressible plastic tubing such as that commercially known as Tygon tubing and which are conventionally used for various medical purposes such as, for example, blood dialysis, clinical monitoring of a patient's blood system, or infusion of various medical fluids into a patient's venous system.
The flow control devices heretofore employed for such purposes generally have been either of complicated construction difficult to fabricate and/or assemble, or particularly in the case where employed in intravascular catheter systems, have necessitated in some circumstances the involved and inconvenient procedure of disconnecting the tubing at one or the other of its ends from either the catheter or supply of medical fluid, then inserting the free end of the elastically deformable plastic tubing endwise into and through the flow control device, and finally reconnecting the free end of the tubing to the catheter or to the supply of medical fluid.
The prior type flow control devices as referred to above, moreover, and more particularly those for regulating the flow of the liquid medium to a certain number of drops per given time unit, generally have not been provided with any so-called memory device for indicating the adjusted setting of the device that provided the desired flow rate of the liquid medium through the tubing system. As a result, when such prior flow control devices were disconnected from the tubing system for some reason or another, for instance, to check the reason for a stoppage of the liquid flow through the tubing system, it then became necessary to manually readjust the setting of the device, generally by trial and error procedure, in order to restore the previous setting of the device so as to provide the same rate of flow of the liquid medium through the tubing as before. Obviously, such a resetting procedure constitutes a time consuming operation and therefore an undesirable characteristic of the prior type fluid flow control devices such as used for medical purposes.